DnsServiceRegister API issue

Question

I'm trying to use the Windows 10+ API DnsServiceRegister to register a web server to be discoverable.

       DNS_SERVICE_REGISTER_REQUEST rd = {};           
       DNS_SERVICE_INSTANCE di = {};
       rd.pServiceInstance = &di;
       rd.unicastEnabled =  0;
       di.pszInstanceName = L"Remote Control._http._tcp.local";
       di.pszHostName = L"192.168.10.6";
       IP4_ADDRESS i4 = {};
       InetPton(AF_INET, L"192.168.10.6", (void*)&i4);
       di.ip4Address = &i4;

       di.wPort = (WORD)12345;
       rd.Version = DNS_QUERY_REQUEST_VERSION1;
       rd.pRegisterCompletionCallback = [](DWORD Status,
           PVOID pQueryContext,
           PDNS_SERVICE_INSTANCE pInstance)
       {
           nop();
       };
       DnsServiceRegister(&rd, 0);

The call succeeds (return value DNS_REQUEST_PENDING as per documentation) and after a while, my callback is called with status = 0 (Success?). However, no UPnP tools detect my service. When I set unicast to 1, status is 9002 (error).

What am I missing in using this API?

Edit: When the callback is called, the pInstance parameter there points to a DNS_SERVICE_INSTANCE with ip4Address and ip6Address null pointers. Why?

Edit: It's discoverable by using DnsServiceBrowse(). But UPnP scan tools don't discover it.